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Project Summary

Difficulty	1
Time required	Very Short (a day or less)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	No issues

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Objective

In this experiment you will test the level of compaction of soil at different locations.

Introduction

Have you ever had to dig a hole in really hard dirt? It is a lot of work! It is much easier to dig a hole in soft, loose soil. Why is that? Soil that is hard and dry is often compacted, which means that it has been packed down solid, making it difficult to penetrate.

Just as it is difficult for you to dig in compacted soil, it is also difficult for soil dwelling organisms, like bugs and worms, to tunnel in compacted soil. You won't usually find many organisms living in compacted soils because they cannot get the air, space and nutrients that they need to survive. Also, compacted soil makes it difficult for plants with delicate root systems to thrive. Very compacted soil tends to support the growth of weeds, which have thick tap roots which penetrate deeply into compacted soil and out-compete other plants.

Which areas are most susceptible to soil compaction? In this experiment you will make an instrument to test different areas to see where the soil is the most compacted. You should test places like gardens, walkways, turf, sunny areas, shady areas moist and dry areas. Where do you think the most compacted soil will be? Can you think of creative ways to avoid soil compaction in these areas?

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• soil type
• soil structure
• porosity
• compaction
• density

• How does soil become compacted?
• How can soil compaction be measured?
• Which areas have the most and least compacted soil?

Bibliography

• RVDE, 2004. "Activities: Soil Compaction" U.S. Geological Survey (USGS), Recovery and Vulnerability of Desert Ecosystems (RVDE) Program. [accessed: 4/28/06]
  http://mojave.usgs.gov/rvde/activ_soilcomp.html
• Petersen, M., Ayers, P. and Westfall, D. 2004. "Managing Soil Compaction,"Colorado State University Cooperative Extension, Agriculture. [accessed: 4/28/06]
  http://www.ext.colostate.edu/PUBS/crops/00519.html
• Brynie, F.H., 2005. Parent's Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 165-168.

Materials and Equipment

• metal knitting needle (size 7 or small enough to fit inside the spool)
• small spool
• metric ruler
• permanent marker
• rubber band

Experimental Procedure

1. Place the needle into the spool to see that it fits.
2. Place the apparatus, pointy side down, onto a table. Mark where the knitting needle sticks out of the top of the spool with your permanent marker. This line will be zero.
3. Tightly wrap a rubber band around the knitting needle and push it towards the non-pointy, capped end of the needle. You will use this to mark the depth of your soil measurements.
4. Choose different locations to test the soil for compaction. Describe each location in a data table. Where is it? What type of soil is there? Is it wet or dry? Are there any plants?
5. At each location place the spool on the ground pointy side down. Push down hard on the knitting needle until it stops moving into the ground. Slide the rubber band down against the top of the spool.



6. Remove the knitting needle from the ground and measure the distance between the line and the rubber band with your ruler.


7. Record the measurement in a data table:

Location	Description	Measurement (cm)
1
2
3
4

8. Where is the soil most compacted? The least compacted? What characteristics did you notice about the most compact soils? What characteristics did you notice about the least compact soils? Think about things like foot traffic, soil type, moisture or plant covering.

Variations

• Try an experiment to investigate the effect of walking on soil and compaction. Dig up some soil so that it is loose. Measure the compaction of the soil with your spool. Now walk over the site and measure again. How did it change? Will it continue to change if you keep repeating the experiment? Why is it important not to walk in a garden bed?
• Do wet or dry soils become more compacted? Add different amounts of water to dry soil. Use a tamper or water roller to compact the soil in each sample. Measure each sample with your spool. Which soils are the most compacted? What happens if you let them dry out and measure them again afterwards?

• For more science project ideas in this area of science, see Geology Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Brynie, F.H., 2005. Parent's Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 165-168.

Last edit date: 2006-08-15 17:10:07

Career Focus

If you like this project, you might want to think about career opportunities in Geology.

Just as a doctor uses tools and techniques, like x-rays and stethoscopes, to look inside the human body, geoscientists explore deep inside a much bigger patient—planet Earth. Geoscientists seek to better understand our planet, and to discover natural resources, like water, minerals, and petroleum oil, which are used in everything from shoes, fabrics, roads, roofs, and lotions to fertilizers, food packaging, ink, roads, and CD’s. The work of geoscientists affects everyone and everything. Learn more about this career: Geoscientist.